Hundreds of convicted murderers in Florida will likely get a chance to convince a judge that their life prison terms should be reduced because they were juveniles when they killed.

A U.S. Supreme Court decision Monday in two cases, Miller v. Alabama and Jackson v. Arkansas, struck down laws in 28 states that mete out mandatory life sentences without the possibility of parole for minors convicted of homicide.

The ruling, hailed by civil-rights activists, doesn’t mean Florida judges can’t still impose a life sentence on youths for first-degree murder — but they must now at least consider a defendant’s age.

“Kids are different. They are very impulsive. They follow other people. They don’t have a full understanding of the consequences of what they’re doing,” said Miami-Dade Assistant Public Defender Stephen Harper, who has worked on the issue and estimates some 225 Florida convicts could get new sentences. “The court found it is important for a judge to consider all these factors.”

Monday’s opinion follows the high court’s 2010 decision, based on a Jacksonville case, that ruled that sentencing minors to life without the possibility of parole in non-homicide cases constituted “cruel and unusual punishment.”

The teen in that case, Terrance Graham, received probation for a robbery, but was later arrested for another armed robbery and sentenced to life in prison for violating probation.

In most states, the Graham ruling meant simply amending a life sentence to include the possibility of parole. But Florida lawmakers abolished parole in 1983, and with 115 defendants affected, the state was in a bind. Many of those 115 defendants have since been re-sentenced, and some have been released from custody.

Monday’s high court decision drew heavily on the reasoning in Graham.

The first case involved Kuntrell Jackson, who as a 14-year-old in 1999 participated in the robbery of an Arkansas video store in which a clerk was shot and killed. Jackson did not fire the weapon, but was convicted of felony murder for participating in an armed robbery that led to a death.

The second case involved Evan Miller, who in 2003 beat an Alabama man to death with a baseball bat. Miller, 14 at the time, had been in and out of foster care because of his tumultuous family life.

Both teens — who under an earlier Supreme Court ruling are not eligible for the death penalty — were charged as adults.

Justice Elena Kagan, in the majority opinion, noted that Miller “deserved severe punishment” but that the automatic life sentence did not allow a judge to consider his troubled past.

The law “prevents taking into account the family and home environment that surrounds him — and from which he cannot usually extricate himself — no matter how brutal or dysfunctional,” Kagan wrote.

The justices who formed the majority were Kagan, Sonia Sotomayor, Ruth Bader Ginsburg, Stephen Breyer and Anthony Kennedy. The dissenters: Samuel Alito Jr., John Roberts, Clarence Thomas and Antonin Scalia.

The American Civil Liberties Union hailed Monday’s ruling.

“Today’s decision helps to restore some rationality to the treatment of juveniles in our criminal justice system,” said Steven R. Shapiro, ACLU national legal director. “Surely, it is not too much to expect that judges will at least consider the fact that a 14-year-old is standing before them when deciding whether to impose a sentence of life imprisonment without the possibility of parole, even in murder cases.”

Miami-Dade Public Defender Carlos J. Martinez said in a statement: “The court continues to recognize what science has been teaching us. Kids are different.”

The Florida Attorney General’s Office, which handles appeals, was not happy.

“We’re disappointed that the Court has disallowed mandatory life imprisonment for juveniles who commit heinous murders,” spokeswoman Jennifer Meale said.

The Florida Department of Corrections was still doing research Monday to determine how many state inmates could be affected by the ruling. Miami-Dade prosecutors are still tallying how many defendants would get new sentencing hearings.

Some inmates in high-profile cases would be eligible, including Michael Hernandez, convicted of murdering a classmate at Southwood Middle School in 2004, and Ronald Salazar, convicted of raping and murdering his 11-year-old sister in 2005. Each was 14 at the time of the crimes.

In Broward, Edward Babbs is eligible for re-sentencing. He was sentenced to life earlier this year in the murder of his pregnant girlfriend outside a Miramar grocery store in 2009; when he committed the crime, Babbs was two months shy of his 18th birthday.

Broward County prosecutors estimate that they have 10 to 15 murder cases that may have to be reviewed in light of the Supreme Court’s ruling.

Jeff Marcus, the chief of the felony division for the Broward County State Attorney’s Office, said the court’s decision could affect any first-degree murder sentences handed down against juveniles since 1994, the year the state adopted mandatory life sentences for first-degree murder.

Lawyers are unsure exactly how the cases will proceed, although prosecutors expect sentencing will be lengthy, with testimony from defense experts.

Marcus said these defendants could potentially be sentenced under the pre-1994 sentencing statute, which carried a 25-year minimum sentence for first-degree murder with a possibility of parole, although the state’s parole commission now exists only to handle pre-1983 cases. More likely, the Legislature will need to craft a new sentencing scheme for juveniles.

Florida Rep. Michael Weinstein, a Jacksonville Republican, said that if he is reelected this fall, he will sponsor a bill to do just that.

Weinstein, a current prosecutor, sponsored a bill in March to allow juveniles convicted of non-homicides and sentenced to life to have their sentences re-visited after 25 years in custody. But the bill died on the Senate floor.

New law is needed, Weinstein said, because judges are “boxed in” between the Supreme Court decisions and laws that now mandate “illegal sentences.”

“The Legislature needs to help the judiciary in setting guidelines for how juveniles are to be processed as adults,” he said.